1. Field of the Invention
The present invention relates generally to tissue treatment systems and in particular to a system and method for promoting the growth of new bone or cartilage tissue by activating dura mater, periosteum or endosteum through the application of reduced pressure.
2. Description of Related Art
Clinical studies and practice have shown that providing a reduced pressure in proximity to a tissue site augments and accelerates the growth of new tissue at the tissue site. The applications of this phenomenon are numerous, but application of reduced pressure has been particularly successful in treating wounds. This treatment (frequently referred to in the medical community as “negative pressure wound therapy,” “reduced pressure therapy,” or “vacuum therapy”) provides a number of benefits, including faster healing and increased formulation of granulation tissue. Typically, reduced pressure is applied to tissue through a porous pad or other manifolding device. The porous pad contains cells or pores that are capable of distributing reduced pressure to the tissue and channeling fluids that are drawn from the tissue. The porous pad often is incorporated into a dressing having other components that facilitate treatment.
Wound healing may be broadly split into three overlapping basic phases: inflammation, proliferation, and maturation. The inflammatory phase is characterized by hemostasis and inflammation. The next phase consists mainly of angiogenesis, granulation tissue formation, collagen deposition and epithelialization. The final phase includes maturation and remodeling. The complexity of the wound healing process is augmented by the influence of local factors such as ischemia, edema, and infection, as well as systemic factors such as diabetes, age, hypothyroidism, malnutrition, and obesity. The rate limiting step of wound healing, however, is often angiogenesis.
In bone and cartilage healing, the periosteum is the primary source of precursor cells that develop into osteoblasts and chondroblasts. The bone marrow, endosteum, small blood vessels and fibrous connective tissue are secondary sources of precursor cells. However, bone and, especially, cartilage healing is often slow and frequently inadequate. For this reason, the medical community has long sought to develop improved methods of tissue repair and replacement for bone and cartilage defects.
With craniofacial defects, successful repair or replacement is greatly compromised without the endogenous osteogenic capacity of the dura mater. Unfortunately, dura mater in humans begins to lose its osteogenic capacity rapidly after humans reach about two years of age. Current reconstructive techniques for craniofacial defects use autogenous, allogeneic, and prosthetic materials to counter the osteogenic deficiency of mature dura mater. Growth factors also are commonly used to facilitate tissue regeneration. These techniques may achieve some functional restoration of craniofacial defects, but all are inherently limited by factors such as donor-site morbidity, unpredictable graft resorption, insufficient autogenous resources, viral disease transmission, immunologic incompatibility, structural failure, unsatisfactory aesthetic results, and cost. Moreover, it has been shown that osteoblasts induced by growth factors are initially derived from undifferentiated mesenchymal stem cells of the dura mater, and later, though limited, augmented by cells in the overlying connective tissue rather than from cells in the cranial bone surrounding the defect. Cytokines or other factors are required to induce bone forming cells derived from the dura and the overlying connective tissue.
Methods that improve healing of bone and cartilage are thus desired. The present invention addresses that need.